1. Field of the Invention The present invention relates to a combustion chamber and to a method for operating the combustion chamber for combustion of nitrogen-containing gas with low NO.sub.x emissions in which combustion chamber there is at least one primary stage for precombustion of a fuel-rich mixture having an air number approximately in the range of .lambda.=0.6 to 0.9, wherein gas and air forming the fuel-rich mixture are supplied to the primary stage via a gas inlet and an air inlet to the combustion chamber or optionally the gas and the air can be premixed and the resultant fuel-rich mixture fed via a mixture inlet to the primary stage wherein partial combustion of the fuel-rich mixture takes place, and at least one succeeding secondary stage in the combustion chamber in open communication with the primary stage for the flow of reaction products from the primary stage to the secondary stage, wherein in the latter post-combustion of the reaction products from the primary stage occurs at high air excess, an air number approximately in the range of .lambda.=1.3 to 2.
2. Description of the Prior Art
In the gasification of coal with oxygen, for instance, a gas having an average calorific value is produced, which contains fuel-bound nitrogen in the form of NH.sub.3 and HCN. Some other fuels also contain nitrogen in bound form. If such a fuel is combusted in a standard combustion chamber, a great deal of NO.sub.x is produced because of the oxidation of the atomic nitrogen set free during combustion. The maximum temperatures in a diffusion flame can also become so high that a great deal of thermal NO.sub.x is produced.
Various ways of solving this problem are known; for instance, NH.sub.3 and HCN can be removed by scrubbing the gas before combustion takes place. However, this involves a considerable expenditure for gas purification.
The following source in the literature provides an overview of the background and field of the prior art in stationary gas turbines:
Final report, "ADVANCED COMBUSTION SYSTEMS FOR STATIONARY GAS TURBINE ENGINES", Volumes I, II, III and IV, by R. M. Pierce et al, Pratty & Whitney Aircraft Group, Government Products Division, United Technologies Corporation, West Palm Beach, Fla. 33402, Contract No. 68-02-2136; prepared for U.S. Environmental Protection Agency, Office of Research and Development, Washington, DC 20460, No. FR-11405, Mar. 31, 1980.
Pages 2 ff. of Volume III of this reference describes a concept for combustion of fuels having bound nitrogen. In this concept, pre-combustion of a fuel-rich mixture first takes place in a primary stage, and then remaining combustion is done with a high air excess in a secondary stage. A pre-mixing chamber is also provided in this concept.
In a publication of the American Society of Mechanical Engineers (ASME), No. 82-GT-29, entitled "Alternative Fuels: Burner Concepts and Emission Characteristics of a Silo Combustor", by W. Krockow and H. Schabbehard, the influence of various procisions on NO.sub.x generation in the combustion of fuel having bound nitrogen is discussed. From this discussion, it is known that a high proportion of inert substances, such as molecular nitrogen, decreases NO.sub.x production. Because of the high calorific value of such a mixture, all the reactions take their course at a low temperature level and hence very slowly. As a result, large combustion chambers having large surface areas are required, which entails cooling problems, or else the rate of recombination of atomic nitrogen into N.sub.2 that is attained is too low.
The above-described combustion in two stages has the advantage that in the first, fuel-rich primary combustion chamber with an air number of =0.6 to 0.9, the fuel decomposes, where-upon N recombines, predominantly to N.sub.2, since only a little NO can be produced because of the oxygen deficiency. Nevertheless, the high temperatures in the primary combustion chamber entail major cooling problems, because inflowing air reacts and generates high temperatures near the wall. When air is admixed for the after-burning in the vicinity of an air number .lambda..apprxeq.1, a very great quantity of thermal NO.sub.x is also produced; nor can this be completely avoided by the rapid admixture of air.
In Volume II of the above-cited reference, "ADVANCED COMBUSTION SYSTEMS . . . ", cooling systems for a primary combustion chamber are described, for instance on pages 10 and 11; however, the provisions described there are costly and also entail various problems, for instance if water is used as a coolant.